Sotion FW07 gear reduced Motor Questions. (Drag E-bike)

[forcefed86]

Built a little E-drag mini-bike with FW07 motor Paired with a FD961800 (race version) and 600a 24s LIPO pack.

Bike is very torquey and performs well, but I believe its very far from peak performance and would like some assistance with suggested gearing for a gear reduced motor. Its a 6900-10000 RPM rated with a 2.52 gear reduction. IS there an ideal ratio to shoot for gearing wise to get at least close to the 9000-1000 rated max rpm?

Started with a 18 motor gear and a 40 rear as I had them laying around and its difficult to find smaller rear gears. Am I thinking correctly in just dividing 40 by 18? So 2.22 then multiply that by 2.52? So a 5.6 gear ratio?

That *seemed* like it was WAY too tall of a gear. Instant wheelies at any speed and instantly smoked tires with even light throttle down low. Bike has wheelie bars etc but it was violent. Uncontrollably so.

So I went with a 17t motor and had a 30t rear gear made. (so a 4.44 ratio?)

This is much more manageable off the starting line, but seems to be out of steam up top. As in so much gear the motor can’t pull past 5600 on the FD APP.

That seems odd because its making 30-40KW. Seems like it should be able to pull much higher motor RPM? Esp. with 24s voltage I’d think.



Am I missing something here? Calculating the final gear reduction incorrectly maybe? Bike is a blast but I feel like there's alot left in it. Would I likely be better going back to the original 40t rear to make it easier for the motor to pull past 5600rpm? Then just adjust the tune up down low to get rid of the violent behavior?

thanks!

 

[dominik h]

How big ist your rear tire?
What was your topspeed?

Are you using weakening field to reach higher rpm.

You can adjust the tourque in the ratios of speed.
Just try starting with 50% in the first three rpms and you will only have 50% of tourque.

 

[forcefed86]

18x10 tire. Top speeds only around mid to low 60's depending on SOC at 5600ish. I have played with weak and it does diddly. Don't really understand that either as I'm very familiar with it and it works great on my QS165 motor. I have everything at 100% weak wise to 5500 then slowly taper it down to 70% by 9k But I never get there. Shows weak is active but it doesn't do much.

I do ramp in power even now to keep in planted. Best of a 1.80 60' time on the draggy on un prep'd asphalt. But even at 30kw you'd think it would pull clean past 5600? I was hesitating to just throw more amps at it, but maybe that's what it needs.

Using 40AH worth of "25C rated" lipo. Figure if im at even half that it should pull 500a clean and even more burst C rating for 10 sec or so. I'm never on the throttle over 10 sec. I'm also afraid to sag these lipos down too far under load and damage them. From what I'm reading the guys that drag race the RC lipos just go by temperature and don't care what the bats sag to. But I'm not willing to damage mine so I have safeties in place.

I was trying to take baby steps is all. Its a handfull as is. I'm pretty tall and its factory wheel base for class racing. What I really need to do is stretch the thing out 3 feet so I can lay down on it a bit.

 

[dominik h]

Which rpm do you see with the rear wheel unloaded.

have you set weak response to zero

Which value is set at LD

Probably the controller is reducing battery current, when the voltage drops to much.
I'm pulling 400A from a 100Ah battery in my scooter and see a drop of 0.5V per cell with 8C continous capable cells.
The 20Ah A123 battery from the Kids kettcar is rated 25C showing a drop of 0.5V per cell during a 500A test.

Probably yours will sag in the same way or even more.
You can run a screen recorder showing the fardriver App during a full power run, then you will see what the controller does and what the battery is doing.

 

[forcefed86]

Will check and report back. I believe I used the RPM that it found when auto learning as I assumed weak was disabled then as well.

Thank you!

 

[SlowCo]

Awesome bike!

 

[j bjork]

I think it will be hard to reach 9-10000 rpm on low-ish voltage. From what I found when measuring was a kv of about 84.
I run 30s and I still find it to loose more power than I expected at higher rpm.
I havent tried with any FW yet, but with mtpa max power seem to be around 4000rpm.
Still very early testing though, I have ridden the bike for 2 hours.

 

[forcefed86]

Appreciate the input, let me know what you find. That KV value would make more sense and aligns more with what I'm seeing. I was hoping to squeak out 85-90mph, as that's pretty much what it needs to finish out the 1/8th mile decently. My other over volted setups around 30s tended to do better with a ton of mech advantage/gear and high rpm. Wondering if this setup would behave the same.

I'm afraid to dump 600a/50kw+ at this motor and risk damage. But I've been told it will take it by a couple people. At least for the 10 sec or less I'm on the throttle. Choices choices! lol

 

[forcefed86]

Strapping down the front end helped a ton. Still feel its nowhere near what it should be capable of but at least it doesn't try to buck me off. I ordered an 18" JR dragster slick to try.

Really hard to get past that 1.9x 60'. Feel like it should be in the 1.6-1.5 zone. Currently at 550 line amps. Still seems to peak out around 5600 rpm.

Did a few 330' hits trying to dial in the wheelie bars. Trouble I'm having is if I lower them enough not to wheelie the whole run they drag the entire 330' pass. Need them at a 1.5" or so off the ground (uneven asphalt) or they drag the whole run. Then I get this silly 330' long wheel stand that won't come down till I let off.